1. Field of Invention
This invention relates to an acoustical switch. More specifically, it relates to a switch which may be closed or opened in response to inaudible blasts on an ultrasonic whistle. The invention is particularly suitable for remotely operating electrical devices, such as household appliances, automatic slide projectors and the like, all of which are controllable by means of electric switches or like components.
2. Prior Art
Remote control systems for electrically operated devices may be generally classified in two types, namely, wired and wireless systems. The wired systems have the obvious disadvantage of relative inflexibility with regard to change of position of either the controlled device or the source of the control signals. As a result, a number of wireless systems have been developed for household use. Among these are the radio frequency systems used for remote control of garage doors from automobiles and the acoustical systems used to control the operation of television sets.
These prior devices have suffered mainly from two deficiencies. First is their relatively high cost. Moreover, they require a special transmitter to be carried by the person who desires to exert control over the system. This transmitter, although portable, is often bulky and, furthermore, represents a substantial item of cost. This latter cost factor is, of course, magnified when independent control by two or more persons is desired.
A principal obstacle against simplifying the transmitter has been the requirement for using signals that are materially different from spurious background signals which might be present in the environment in which the switch is situated. These spurious signals have a tendency to exert unwanted control over the switch.
The prior art devices for remote control of appliances connected to power lines or other fixed and nonportable power supplies cannot be used away from such power sources. Furthermore, the circuits of some of these prior devices are electrically quite complex, which prevents their use in an environment where shocks and vibrations are present.
We are also aware of a remotely actuatable switch that responds to acoustical signals in the upper audible or lower ultrasonic region. However, this requires an expensive, fragile receiving microphone and is not suitable for rugged use. The present invention is directed toward a switch operating on somewhat similar principles, but which is more rugged and simpler to make. These attributes are particularly important if the switch is to be a reliable, low-cost consumer item.